• Journal of Korean Society of Water and Wastewater
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• v.12 no.4
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• pp.86-96
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• 1998

In this study, an intermittently aerated activated sludge process, modified process from conventional activated sludge process, was developed to treat high strength swine wastewater, which has been blamed as major pollutant for stream pollution. Therefore, the optimum cycle for oxic and anoxic period, SRT, and OLR were studied as design parameters. The effects of different time interval for oxic and anoxic period on nitrification and denitrification were examined by operating two reactors with 60/60min and 60/90min as oxic/anoxic period. Although the reactor with 60/60min showed complete denitrification of $NO_x-N$ generated during oxic period, the reactor with 60/90min showed incomplete nitrification due to the inactivity of nitrifier by accumulated $NH_3-N$ toxicity during anoxic period. Therefore, it is recommended to operate same interval for oxic and anoxic period. In order to determine the optimum cycle for oxic/anoxic period, four different reactors with 30/30, 60/60, 90/90 and 120/120min were examined. The reactor operation with 90/90min was optimum to get the most stable results in this study. However, the optimum cycle for oxic and anoxic period should be changed with characteristics of influent wastewater and operating conditions. According to lie operation results of three reactors with SRT of 15, 20 and 30days. The reactor with 2Odays SRT showed best removal efficiency of T-N. The optimum OLR would be $2.5Kg\;COD/m^3/day$ which showed the most stable nitrification and denitrification. Since characteristics of influent wastewater in the real system has a severe fluctuation, so it is very difficult to determine each interval for oxic and anoxic period. Therefore, ORP curves, describing the change of oxidation/reduction potential in reactor, can be used as a control parameter for automatic control of oxic and anoxic period. In other words, bending point (Nitrate Knee) of ORP curve during anoxic period could be used as a starting point of oxic period.

• Journal of Korean Society on Water Environment
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• v.24 no.3
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• pp.383-390
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• 2008

Recently, the interests on economical nitrogen removal from wastewater are growing. As a method of the novel nitrogen removal technology, nitrogen removal via nitrite pathway by selective inhibition of free ammonia and free nitrous acid on nitrite oxidizing bacteria have been intensively studied. The inhibition effects of free ammonia and free nitrous acid are low when domestic wastewater is used, however, because of its relatively lower nitrogen concentration than the wastewater from industry and landfill, etc. In this study, a sequencing batch reactor (SBR) is proposed for nitrogen removal to investigate the effect of the low nitrogen concentration on nitrite accumulation. Nitrification efficiency reached almost 100% during the aerobic cycle and the maximum specific nitrification rate ($V_{max,nit}$) reached $17.8mg\;NH_4{^+}-N/g\;MLVSS{\bullet}h$. During the anoxic cycle, average denitrification efficiency reached 87% and the maximum specific denitrification rate ($V_{max,den}$) reached $9.8mg\;NO_3{^-}-N/g\;MLVSS{\bullet}h$. From the analysis the main reason of nitrite accumulation in the SBR was free nitrous acid rather than free ammonia. Nitrite accumulation increased with the decrease of organic content in the wastewater and the mechanism is not well understood yet. From the result of fluorescent in situ hybridization, the distribution of nitrite oxidizing bacteria was in equilibrium with ammonium oxidizing bacteria when nitrite accumulation did not occur.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.1
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• pp.15-25
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• 2006

This study was initiated to evaluate the effect of HRT(hydraulic retention time) on removal efficiencies of organic matter (C), nitrogen(N) and phosphorus(P) in municipal wastewater for suspenced-growth processes(MLE; Modified Ludzack-Ettinger) and hybrid process(Modified-Dephanox). M-Dephanox process was designed to improve the performance of Dephanox process on denitrification efficiency. As the results, removal efficiencies of C, N and P in M-Dephanox process, which is hybrid process, were higher than those in MLE, which is suspended-growth process. Especially, nitrification inhibition of MLE was observed more severely than M-Dephanox as hydraulic retention time was reduced from 6 hr to 3.5 hr. Nitrification in nitrification reactors on M-Dephanox, at short HRT, was so excellent that ammonia nitrogen removal efficiency in nitrification reactors of M-Dephanox was about 92% at 1.59 hr of HRT of nitrification reactors, however, nitrification in nitrification reactors on M-Dephanox was affected severely by organic matter entering to nitrification reactors from downstream settler. It was observed that reducing of HRT in whole process resulted from reducing of HRT in nitrification reactors on M-Dephanox.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.2
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• pp.220-228
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• 2007

In this study, effective simultaneous nitrification and denitrification reaction was accomplished in a completely mixed single bioreactor. As the important factors on the reaction, optimal DO concentration and effective range of influent C/N ratio was investigated with the synthetic wastewater. Experimental results show that stable nitrogen removals were accomplished with 0.5 mg/L DO concentration and over 7 C/N ratio. Nitrogen removal efficiency of the real municipal wastewater was low with 0.5 mg/L DO concentration because of its low C/N ratio. The increment of the C/N ratio at the inflow of the municipal wastewater with addition of external carbon source (glucose) over 7(up to 14) shows over 70% nitrogen removal in the single bioreactor.

• Asian-Australasian Journal of Animal Sciences
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• v.28 no.6
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• pp.896-902
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• 2015

Milking center wastewater (MCW) has a relatively low ratio of carbon to nitrogen (C/N ratio), which should be separately managed from livestock manure due to the negative impacts of manure nutrients and harmful effects on down-stream in the livestock manure process with respect to the microbial growth. Simultaneous nitrification and denitrification (SND) is linked to inhibition of the second nitrification and reduces around 40% of the carbonaceous energy available for denitrification. Thus, this study was conducted to find the optimal operational conditions for the treatment of MCW using an attached-growth biofilm reactor; i.e., nitrogen loading rate (NLR) of 0.14, 0.28, 0.43, and $0.58kg\;m^{-3}\;d^{-1}$ and aeration rate of 0.06, 0.12, and $0.24\;m^3\;h^{-1}$ were evaluated and the comparison of air-diffuser position between one-third and bottom of the reactor was conducted. Four sand packed-bed reactors with the effective volume of 2.5 L were prepared and initially an air-diffuser was placed at one third from the bottom of the reactor. After the adaptation period of 2 weeks, SND was observed at all four reactors and the optimal NLR of $0.45kg\;m^{-3}\;d^{-1}$ was found as a threshold value to obtain higher nitrogen removal efficiency. Dissolved oxygen (DO) as one of key operational conditions was measured during the experiment and the reactor with an aeration rate of $0.12\;m^3\;h^{-1}$ showed the best performance of $NH_4-N$ removal and the higher total nitrogen removal efficiency through SND with appropriate DO level of ${\sim}0.5\;mg\;DO\;L^{-1}$. The air-diffuser position at one third from the bottom of the reactor resulted in better nitrogen removal than at the bottom position. Consequently, nitrogen in MCW with a low C/N ratio of 2.15 was successfully removed without the addition of external carbon sources.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.2
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• pp.81-96
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• 2011

Sediment oxygen demand(SOD) and denitrification rates were measured in four major estuaries(Suncheon Bay, Seomjin river estuary, Goseong stream estuary and Masan Bay) in south coast of Korean peninsula from March of 2009 to May 2010 to estimate organic matter cleaning capacity. SOD was estimated from the temporal dissolved oxygen concentration change and isotopic pairing technique was employed to measure denitrification. Sediment oxygen demand(SOD) was ranged from -5.1 to 24.6 mmole $O_2m^{-2}d^{-1}$ and denitrification rate was ranged from 0.0 to 3.9 mmole $N_2m^{-2}d^{-1}$in the study area. SOD was the highest in Masan Bay(-2.2 to 19.2, average = 10.2 mmole $O_2m^{-2}d^{-1}$) and Suncheon, Goseong, Tae-an and Seomjin followed. Denitrification was also the highest in Masn Bay(0.0 to 3.9, average = 1.0 mmole $N_2m^{-2}d^{-1}$) and Goseong, Seomjin, Suncheon and Taean followed. The effect of benthic photosynthesis by microphytobenthos on denitrification was evident in some season of Tae-an, Seomjin, and Masn Bay. The increased oxygen level produced by photosynthesis stimulated nitrification without severe adverse effect on denitrification and, as a result, coupled nitrification and denitrification was enhanced in these areas. A difference of seasonal patterns of denitrification at each site depended on relative importance of denitrification on different nitrate source($D_w$: nitrate from water column and $D_n$: nitrated produced during nitrification). Denitrification was maximum during spring in Goseong, Suncheon and Masan Bay. On the contrary, denitrification was the highest during summer in Tae-an and Seomjin estuary.

• Journal of the Korea Organic Resources Recycling Association
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• v.16 no.2
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• pp.74-80
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• 2008

Removal of nitrogen compound under nitrification related with denitrification by biofilm which developed on the porous media was investigated. With the investigation of $NH_4-N$ nitrification and autotrophic denitrification supplied with sulfur media as electron donor, conclusions were retrieved as follows. When $F/M_N$ ratio of $NH_4-N$ was increased from $0.0062-0.034gNH_4-N/g\;MLVSS{\cdot}day$ by the change of influent concentration and HRT the nitrification rate decreased as the increase of loading rate. Also under the same conditions of $F/M_N$ ratio, the alkalinity consumption rate of operation was higher at 8 hours of HRT than at 6 hours of HRT. Accordingly the influent loading rate variation by detention time with influent flow influenced more on the nitrification efficiency than the influent loading rate variation by the influent concentration did. Denitrification rate with various EBCT(Empty Bed Contact Time) showed average 25% at 8.4hrs of EBCT but sharply decreased average 5% at 4.6hrs of EBCT, so the operation would be more effective at above 8.4hrs of EBCT. Also denitrification rate was known to be adversely increased as $NO_3-N$ loading rate per unit volume of sulfur-media was decreased within the range of $0.5{\sim}2.0kgNO_3-N/m^3{\cdot}day$.

• Journal of Environmental Science International
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• v.13 no.3
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• pp.245-250
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• 2004

The SBR(Sequencing Batch Reactor) process is ideally suited to treat high loading wastewater due to its high dilution rate. SBR operates by a cycle of periods consisting of filling, reacting, settling, decanting and idling. The react phases such as aeration or non-aeration, organic oxidation, nitrification, denitrification and other bio-logical reactions can be achieved in a reactor. Although the whole reactions can be achieved in a SBR with time distributing, it is hard to manage the SBR as a normal condition without recognizing a present state. The present state can be observed with nutrient sensors such as ${NH_{4}}^{+}-N$, ${NO_{2}}^{-}-N$, ${NO_{3}}^{-}-N} and ${PO_{4}}^{ 3-}-P.$ However, there is still a disadvantage to use the nutrient sensors because of their high expense and inconvenience to manage. Therefore, it is very useful to use common on-line sensors such as DO, ORP and pH, which are less expensive and more convient. Moreover, the present states and unexpected changes of SBR might be predicted by using of them. This study was conducted to get basic materials for making an inference of SBR process from ORP(oxidation reduction potential) of synthetic wastewater. The profiles of ORP, DO, and pH were under normal nitrification and denitrification were obtained to compare abnormal condition. And also, nitrite and nitrate accumulation were investigated during reaction of SBR. The bending point on ORP profile was not entirely in the low COD/NOx ratio condition. In this case, NOx was not entirely removed, and minimum ORP value was presented over -300mV. Under suitable COD/NOx ratio which complete denitrification was achieved, ORP bending point was observed and minimum ORP value was under -300m V. Under high COD/NOx ratio, ORP bending point was not detected at the first subcycle because of the fast denitrification and minimum ORP value was under -300mV at the time.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.7
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• pp.479-484
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• 2013

This study was performed to examine the effect of copper on the biodegradability, nitrification, denitrification and oxygen uptake rate (OUR) using batch reactor and continuous flow stirred tank reactor (CSTR) of anaerobic/anoxic/oxic ($A_2/O$). The results of this study can be summarized as follows. In the case of the effect of copper on organic treatment, the bad effect initiated when it was above 4.5 mg/L copper with batch reactor and above 2.0 mg/L copper with CSTR. Concerning the case on nitrification and removal of nitrogen, it showed bad effect when copper was above 4.5 mg/L with batch reactor for nitrification and 1.0 mg/L with CSTR for the removal of nitrogen. The bad effect on the removal of phosphorus began when it was 4.5 mg/L copper with batch reactor and 2 mg/L copper with CSTR. In the case of OUR, it decreased as microbial activity was affected when copper concentration was above 1.5 mg/L in both case of batch reactor and CSTR.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.5
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• pp.547-555
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• 2009

The objectives of this research were focused on the effects of various operating parameters on nitrous oxide emission such as C/N ratio, ammonia concentration and HRT in the hybrid and suspension reactors. With the decreasing of C/N ratios, $N_2O$ emission rates in the both processes were increased because organic carbon source for denitrification was depleted. In case of biofilm reactor operated using medium, $N_2O$ release from the nitrification was not affected by the variation of ammonia concentration. But in the suspension reactor, $N_2O$ production from the nitrification was rapidly increased with the increase of ammonia. Nitrite accumulation caused by undesirable nitrification conditions could be a important reason for the increase in the $N_2O$ production from the aerobic reactor. And rapid increase in $N_2O$ production was reflected by the decrease of HRT, similar to the results observed in the results of ammonia loading changes. So it could be said that it is very important to put in consideration both its optimum conditions for wastewater treatment efficiency and suitable conditions for $N_2O$ diminish, simultaneously, in order to development an eco-friendly and advanced wastewater treatment, especially in BNR process.